1. Field of the Invention
The present invention relates to signal generating circuits, and particularly to a circuit which can quickly generate a PG (power good) signal to a motherboard.
2. General Background
An electronic device such as a computer generally includes many circuits to control apparatuses or elements installed in the computer. When a function is executed, relating circuits must respectively work and respond in a predetermined order in response to certain indicating signals. For example, in a motherboard of the computer, a PG (power good) signal is a signal informing the motherboard that a corresponding apparatus or element is ready for work.
Referring to FIG. 3, a conventional PG signal generating circuit includes a first transistor Q200, a second transistor Q300, an input Pin connected to a base of the first transistor Q200, an output Pout connected to a collector of the second transistor Q300, a first power supply Vcc12 connected to a collector of the first transistor Q200, a second power supply Vcc22 connected to a collector of the second transistor Q300, and the emitters of the first and second transistors Q200 and Q300 are grounded. When a control signal P (high level) is received by the input Pin, the first transistor Q200 turns on and the second transistor Q300 turns off and a PG signal (high level) is sent from the output Pout. However, the more electronic elements there are, the more control signals P there are sent to the PG signal generating circuit which slows the generation of PG signals.
What is desired, therefore, is circuit which can quickly generate a PG signal.